1. Field of the Invention
This invention relates to a process for sterilization, using peracid vapors as the sterilizing agent. It particularly relates to the use of a peracid sterilant vapor capable of contributing a partial pressure of at least about 1 torr to the total vapor pressure achieved during vaporization of the peracid agent in the sterilizing environment during at least the initial stage of the sterilization process. A preferred acid is peracetic acid. The invention has utility generally in public health care areas, such as medicine, dentistry, and other health care delivery areas not only for sterilizing materials and equipment to be used on patients but also for decontamination and/or sterilizing waste, particularly medical waste, to be disposed of as well.
2. Description of the Related Art
The art described herein is not intended to constitute an admission that any patent, publication or other information referred to herein is "prior art" with respect to this invention, unless specifically designated as such.
Contact with high pressure steam is universally recognized as an effective method for bringing about sterilization and it is extensively used. However, the high temperatures of the process (120-132.degree. C.) preclude its use with heat sensitive materials. Furthermore, high temperature steam is corrosive to some metals, notably cutting edges, thus further limiting usefulness of high pressure steam. These facts have contributed to the development of cold sterilization methods.
Cold sterilization is a term used collectively for a number of different procedures which effect sterilization at temperatures substantially below those of the steam process. In one form of cold sterilization, the object to be treated is brought in contact with a liquid sterilant formulation. Among the limitations of this procedure is that the sterilant must then be removed from the sterilized object, generally by extensive washing under sterile conditions. Also, steps must be taken to protect personnel and environment from the liquid sterilant, thereby increasing the cost and complexity of the process.
Another form of cold sterilization utilizes a sterilant in the gas phase. The most widely used gas sterilant is ethylene oxide (ETO). ETO is a very effective antimicrobial agent. It penetrates most materials well. It does not destroy the structural integrity of a wide range of device materials. Among its disadvantages is that it is highly flammable, even explosive. Flame retardants are generally incorporated into the ETO sterilant formulation, frequently to the extent of 88% or 90%. A common flame retardant for ETO is Freon 12, a substance believed to be involved in the destruction of the earth's ozone layer. Environmental concerns have brought about severe regulations in the use of Freon 12. Its availability for future use in sterilization is at best unlikely. Carbon dioxide has been proposed as an alternative to Freon 12, but its use introduces a number of new problems. Other alternatives have been considered, but none have been shown to be satisfactory to date. The use of ETO as a gas sterilant is further complicated by the fact that ETO readily polymerizes, forming undesirable films on equipment and the load to be sterilized, and that its emission or retention in the load poses serious health hazards. Careful monitoring and very long aeration times are required. As a consequence of the many problems surrounding the use of ETO, an alternative cold sterilant is eagerly sought by the industry.
Ozone, or more precisely, a mixture of oxygen and ozone, has been proposed as a gaseous sterilant. Such a mixture is generated as needed by passing an electric discharge through a stream of oxygen. The effectiveness of ozone as a biocide has been known for many years. It has been used in water purification and in treating air in confined spaces. Ozone is a highly reactive oxidizing agent and as such is not very selective as a sterilant. It attacks a number of structural materials, notably natural gum rubber, several metals and some common plastics during the course of sterilization. Its general usefulness as a cold sterilant has not been fully established.
Hydrogen peroxide in the vapor phase has recently been proposed for cold sterilization. Like ozone, hydrogen peroxide is a highly reactive oxidizing agent. It has been reported to attack cellulosic wrapping materials which are commonly used in sterilization, necessitating the use of special wrapping materials. Also, various materials in the load to be sterilized appear to be penetrated to different degrees, and surface contaminants consume unpredictable amounts of the sterilant vapor. Its general usefulness remains to be established.
Formaldehyde in various formulations was used fairly extensively as a fumigant, disinfectant and sterilant. Reported carcinogenicity has severely restricted its utility.
The use of peracids in liquid form as a sterilant is known. Some initial experimental work has also been done with peracetic acid vapor in which its sterilant effect has been noted. However, no one has yet provided a practical process for using peracid vapor in vapor sterilization.